Older women are usually considered at greater risk of pregnancy complications than younger women. However, when it comes to stroke during pregnancy, a new study suggests it is younger women who are most at risk.

Researchers find younger women are more than twice as likely to experience stroke during or just after pregnancy than their non-pregnant counterparts.

Researchers found that pregnant older women had a similar stroke risk as their non-pregnant counterparts, while younger pregnant women were found to be at more than double the risk of stroke than non-pregnant women of the same age.

Lead study author Dr. Eliza C. Miller, of the Department of Neurology at Columbia University Medical Center (CUMC) in New York, and team published their findings in JAMA Neurology.

Each year, around 795,000 people in the United States are affected by stroke, and it is the cause of more than 130,000 deaths.

It is well known that pregnancy can raise stroke risk; gestational diabetes, high blood pressure, and increased bleeding after birth are all factors that can make expectant mothers more susceptible to stroke.

According to Dr. Miller and colleagues, stroke affects around 34 in every 100,000 pregnancies in the United States, and this number is on the increase.

“The incidence of pregnancy-associated strokes is rising, and that could be explained by the fact that more women are delaying childbearing until they are older, when the overall risk of stroke is higher,” notes senior study author Dr. Joshua Z. Willey, assistant professor of neurology at CUMC.

“However,” he adds. “very few studies have compared the incidence of stroke in pregnant and non-pregnant women who are the same age.”

Assessing stroke risk by age at pregnancy

For their study, Dr. Miller and team set out to determine the risk of stroke during pregnancy by age.

Using data from the New York State Department of Health Statewide Planning and
Research Cooperative System (SPARCS) inpatient database, the researchers were able to pinpoint 19,146 women in New York State aged 12-55 years who had been hospitalized for stroke between 2003-2012.

Of these women, 797 (4.2 percent) were pregnant or had given birth in the last 6 weeks.

The researchers looked at the incidence of stroke for both pregnant and non-pregnant women across four age groups: 12-24 years, 25-34 years, 35-44 years, and 45-55 years.

Overall, the team found that stroke incidence increased with age; there were 14 stroke events per 100,000 pregnant or postpartum women aged 12-24, while the stroke events for pregnant or postpartum women aged 45-55 were 46.9 per 100,000.

Stroke risk doubled for younger expectant mothers

However, when it came to assessing stroke risk relative to non-pregnant women, the team found younger women fared worse.

Among women aged 25-34, pregnant or postpartum women were 1.6 times more likely to have a stroke event than non-pregnant women of the same age, the team reports.

However, among women aged 35-44, stroke incidence among pregnant or postpartum women was comparable to that of non-pregnant women, at 33 per 100,000 and 31 per 100,000, respectively.

Among women aged 45-55, stroke incidence was higher for non-pregnant women, at 73.7 per 100,000, compared with 46.9 per 100,000 for pregnant or postpartum women.

Based on their findings, Dr. Miller and team say it is perhaps time to increase focus on identifying and reducing stroke risk among younger pregnant women.

“We have been warning older women that pregnancy may increase their risk of stroke, but this study shows that their stroke risk appears similar to women of the same age who are not pregnant.

But in women under 35, pregnancy significantly increased the risk of stroke. In fact, 1 in 5 strokes in women from that age group were related to pregnancy. We need more research to better understand the causes of pregnancy-associated stroke, so that we can identify young women at the highest risk and prevent these devastating events.”

Dr. Eliza C. Miller

The researchers stress that their results should be “interpreted with caution regarded and primarily as hypothesis generating.”

Still, the team concludes that while older expectant mothers are at greater risk of numerous pregnancy complications, “a higher risk of stroke may not be one of them.”